Advanced semiconductor circuitry may use various programmable interconnect elements to connect logic blocks for a number of applications, such as electrically programmable feature selection, speed sorting, die identification, and redundancy implementation. For high-speed applications, the on-state of such structures should have a low resistance. To achieve a high density of such structures in an integrated circuit, the programmable elements should be small.
Programmable fuses are an example of a programmable element, wherein, for example, a fuse element, e.g., sacrificial metal lines buried in a dielectric layer in the circuits (which are normally closed) are blown by vaporizing the fuse element with laser energy to open the circuit that is not selected. Electrically programmable fuses may be used, for example, for chip ID, redundancy, and non-volatile memory programming.
Current electronic fuses may use melting and/or evaporation of material for programming. For example, programmable fuses fall into at least three categories depending on the method of programming. The first category includes laser-blown fuses where the programmable fuses are programmed using a laser to burn or sever the conductive portion of the fuse. The second category includes electrically blown fuses where the fuse is programmed by passing current through it sufficient to overload and open or burn out the fuse. The third category includes electrically blown anti-fuses, where the fuse is programmed with an electric current, which reduces the resistance across the fuse.
However, the damage associated with these processes may affect neighboring devices, and degrade functionality. For example, in all of these methods of fuse programming, the area surrounding the fuse may be damaged during the programming process due to the heat involved in the programming step. Thus the fuses may require sufficient space between one another on a wafer so that the programming of one fuse does not damage adjacent fuses. However, such configurations reduce a fuse density.
More specifically, laser fusing may produce damage to the area surrounding the fused element, which is traded off for fuse blow yield. Another problem with laser fusing is that it requires a large on-chip area to handle laser power capability as well as “line-of-sight” for laser access (which is a component of the area penalty of the laser fusing process). Additionally, excessive laser energy can cause silicon substrate damage or massive crater formation that impacts neighboring links. Such problems with laser fusing are not necessarily mitigated by traditional electrically blown fuses because electrically blown fuses typically require a larger voltage than is conveniently available on the chip.
Additionally, current electronic fuses (e.g., electrically blown fuses) use silicided polysilicon (from the gate stack), wherein programming is achieved by agglomerating the silicide by passing a high current through the fuse. However, one problem with this approach is that metal gates are now being used in advanced devices, so a new electronic fuse structure is required. That is, a electrical programming method and structure is needed which is compatible with metal gates, while minimizing damage to neighboring structures.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.